1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel capable of preventing air from flowing into an image display part of a liquid crystal display panel where a thin film transistor array substrate and a color filter substrate are attached to each other.
2. Discussion of the Related Art
In general, a liquid crystal display apparatus is a display device where data signals including image information are individually supplied to unit pixels arranged in a matrix form, and the light transmittance of the unit pixels is controlled to display a desired image.
Thus, the liquid crystal display device includes a liquid crystal display panel where the unit pixels are arranged in a matrix form, and a driver integrated circuit (IC) for driving the unit pixels.
In the liquid crystal display panel, a thin film transistor array substrate and a color filter substrate are attached to each other so as to face into each other and have a certain interval (generally, referred to as a cell-gap) therebetween, and, at the cell-gap, a liquid crystal layer is formed.
The thin film transistor array substrate and the color filter substrate are attached to each other by a seal pattern formed along the outer edge of an effective image display part. At this time, on the thin film transistor array substrate or the color filter substrate, a spacer is formed thereby forming a certain cell-gap therebetween.
At outer surfaces of the substrates, a polarizing plate, a retardation plate and the like are installed. Such a plurality of components are selectively constructed thereby varying an advancing state of light and a refraction ratio and thus constructing a liquid crystal display device having a high brightness and a contrast characteristic.
At the liquid crystal display panel where the thin film transistor array substrate and the color filter substrate face into and are attached to each other, a common electrode and a pixel electrode are formed, and apply an electric field to the liquid crystal layer. That is, a voltage applied to the pixel electrode is controlled in a state of applying a voltage to the common electrode, whereby a light transmittance of the unit pixels can be individually controlled. In order to control the voltage applied to the pixel electrode by the unit pixels, a thin film transistor used as a switching device is formed at each unit pixel.
The liquid crystal display device is generally divided into a twisted nematic (TN) mode liquid crystal display panel and an in-plane switching (EPS) mode liquid crystal display panel.
In the TN mode liquid crystal display panel, a pixel electrode is formed on a thin film transistor array substrate unit pixel by unit pixel, and a common electrode is formed at an entire surface of a color filter substrate. Thus, a liquid crystal layer is driven by an electric field between the pixel electrode formed on the thin film transistor array substrate and the common electrode formed on the color filter substrate.
At the IPS mode liquid crystal display panel, a pixel electrode and a common electrode are formed on a thin film transistor array substrate at a certain interval therebetween. Thus, a liquid crystal layer is driven by a horizontal electric field between the pixel electrode and the common electrode formed on the thin film transistor array substrate.
FIG. 1 is an exemplary view illustrating a plane structure of a liquid crystal display panel where the thin film transistor array substrate and the color filter substrate face into and are attached to each other.
In FIG. 1, the thin film transistor array substrate 101 faces into and is attached to the color filter substrate 102, and an edge of one long side thereof and an edge of one short side thereof are protruded compared to the color filter substrate 102.
At a region where the substrates 101 and 102 are attached to each other, an image display part 113 where unit pixels are formed in a matrix form to display an image is provided, and a seal pattern 116 is formed along the outer edge of the image display part 113.
At an edge region of one short side of the thin film transistor array substrate 101 protruded compared to the color filter substrate 102, a gate pad part 114 connected with gate lines of the image display part 113 is provided.
At an edge region of one long side of the thin film transistor array substrate 101 protruded compared to the color filter substrate 102, a data pad part 115 connected with data lines of the image display part 113 is provided.
The gate pad part 114 supplies a scan signal supplied from a gate driver integrated circuit to the gate lines of the image display part 113, and the data pad part 115 supplies image information supplied from a data driver integrated circuit to the data lines of the image display part 113.
On the thin film transistor array substrate 101, the gate lines to which the scan signal is applied, and the data lines to which the image information is applied, intersect one another, so that the unit pixels are defined in a matrix form. At the intersection, a thin film transistor is provided for switching the unit pixel.
On the color filter substrate 102, a red, green or blue color filter corresponding to a unit pixel is provided, and a black matrix is provided to prevent a leakage of light generated from a back-light and prevent a color mixture of the adjacent unit pixels.
In case of the TN mode liquid crystal display panel, a pixel electrode is provided at the thin film transistor array substrate 101, and a common electrode is provided at the color filter substrate 102 to drive a liquid crystal layer. In case of the IPS mode liquid crystal display panel, a pixel electrode and a common electrode are provided at the thin film transistor array substrate 101 to drive a liquid crystal layer.
The thin film transistor array substrate 101 and the color filter substrate 102 are provided with a cell-gap therebetween generated by a spacer so as to be separated from each other, by a constant distance. The substrates are attached to each other by a seal pattern 116 formed at the outer edge of the image display part 113 to form a liquid crystal display panel 100. At one side of the seal pattern 116, a liquid crystal injection hole is provided for injecting liquid crystal between the thin film transistor array substrate 101 and the color filter substrate 102 that are attached to each other. The liquid crystal injection hole is sealed after the injection of the liquid crystal is complete.
The cell-gap between the thin film transistor array substrate 101 and the color filter substrate 102 is constant in the image display part 113, but varies in the region where the seal pattern 116 is formed, because as the sealant is pressed by the pressure generated when the thin film transistor array substrate 101 and the color filter substrate 102 are attached to each other the sealant spreads out.
Accordingly, in order to prevent the cell-gap distance from varying at the seal pattern 116, a glass fiber or a glass ball is added into the sealant as a support member for maintaining the cell-gap. At this time, the glass fiber or the glass ball is added to the sealant at a weight ratio of about 1%.
FIG. 2 is an exemplary view illustrating a sectional structure of a color filter substrate for a region ‘A’ of FIG. 1 in case of the related IPS art mode liquid crystal display panel.
With reference to FIG. 2, a color filter substrate of an IPS mode liquid crystal display panel includes a black matrix 202 made of a resin material, patterned at a region constantly separated from one end portion of a transparent substrate 201 and at a boundary region of pixels to prevent a leakage of light generated from a back-light, and preventing a color mixture of adjacent pixels; a red, green, or blue color filter 203 formed to partially overlap with the black matrix and correspond to a unit pixel; an over-coat layer 204 formed at an entire surface of an upper portion of the transparent substrate 201 including the black matrix 202 and the color filter 203; and a seal pattern 206 formed at an upper surface of the over-coat layer 204 formed on the edge of the transparent substrate 201 so as to partially overlap with the black matrix 202.
The black matrix 202 formed at the color filter substrate of the IPS mode liquid crystal display panel is made of a resin material.
The over-coat layer 204 is formed on an entire surface of an upper portion of the black matrix 202 and the color filter 203 to planarize a surface. That is, because a black matrix 202 is formed of an organic film such as a resin material and is applied as a thick film, the over-coat layer 204 formed of an organic material prevents a deficiency in driving a liquid crystal layer caused by a step difference occurring at a region where the black matrix 202 and the color filter 203 overlap with each other.
As stated above, a glass fiber or a glass ball is added to the seal pattern 206 as a support member for maintaining a cell-gap at a weight ratio of about 1% to a sealant.
FIG. 3 is an exemplary view illustrating a magnified view of the distribution of glass fiber added at to the seal pattern 206 a weight ratio of about 1%.
In the case in which the seal pattern 206 is formed on an upper surface of a black matrix 202 or over-coat layer 204 the glass fiber added to the seal pattern generates a crack at interfaces between the seal pattern 206 and the over-coat layer 204 and between the over-coat layer 204 and the black matrix 202 when outer pressure is generated in attaching the two substrates, or when the attached substrates are examined in a condition of a high temperature and a high humidity after the attaching process. Because of this, the black matrix 202 or the over-coat layer 204 are depressed, and outer air is flowed into the image display part, thereby occurring the deficiency in the liquid crystal display panel. These will be described in detail with reference to exemplary views of FIGS. 4a and 4b. 
FIGS. 4a and 4b illustrate an organic film black matrix 302 formed of a resin material, patterned at a region constantly separated from one end portion of a first transparent substrate 301 and at a boundary region of pixels to prevent a leakage of light generated from a back-light, and preventing a color mixture of adjacent pixels; a red, green or blue color filter 303 formed so as to partially overlap with the black matrix 302 and correspond to a unit pixel; an over-coat layer 304 formed of an organic film and at an entire surface of an upper portion of the first transparent substrate 301 including the black matrix 302 and the color filter 303; a seal pattern 306 formed at an upper surface of the over-coat layer 304 formed on an edge region of the first transparent substrate 301 so as to partially overlap with the black matrix 302; and a glass fiber 307 added to the seal pattern 306, and maintaining a cell-gap at a region where the seal pattern 306 is formed. At this time, the glass fiber 307 has a diameter which is the same as or greater than the cell-gap.
First, as shown in FIG. 4a, in a normal state, the glass fiber 307 added to the seal pattern 306 can maintain a cell-gap by coming in contact with a thin film transistor array substrate (not shown) and the over-coat layer 304 therebetween.
However, as shown in FIG. 4b and as stated above, as the glass ball or the glass fiber 307 is pressed by the outer pressure caused during or after attaching a liquid crystal display panel, the black matrix 302 and the over-coating layer 304 formed of an organic film material are compressed. When the black matrix 302 and the over-coat layer 304 formed of an organic film material are compressed, a crack is generated at an interface between the seal pattern 306 and the over-coat layer 304 and between the over-coat layer 304 and the black matrix 302. Because of this outside air is flowed into an image display part, whereby a deficiency occurs in the liquid crystal display panel, and the seal pattern 306 is broken.
In addition, a crack may be generated at an interface between the seal pattern 306 and the over-coat layer 304 and between the over-coat layer 304 and the black matrix 302 by expansion and contraction according to a temperature of the black matrix 302 and the over-coat layer 304 formed of the organic film material. Because of this outside air flows into the image display part, creating defects in the liquid crystal panel and breaking the seal pattern 306.
As stated above, a glass fiber or a glass ball is added as a support member for maintaining a cell-gap in the seal pattern 306 generally at about 1% of a weight ratio to a sealant and is distributed as shown in an exemplary view of FIG. 3. At this time, 550 or more glass fibers or glass balls are distributed per a unit area of 1 mm×1 mm on the average.
As so far described, in the related art IPS mode liquid crystal display panel, the glass fiber or the glass ball used to maintain the cell-gap between the thin film transistor array substrate and the color filter is added to the seal pattern attaching the thin film transistor array substrate and the color filter substrate at a weight ratio of about 1% to a sealant. Accordingly, when external pressure is generated in attaching the two substrates to each other, or when the attached substrates are examined in a condition of a high temperature and a high humidity after the attaching process, outside air flows into the image display part, causing defects in the liquid crystal display panel or breaking the seal pattern.